Thankfully never encountered either jellyfish or great whites in Sussex waters...yet.
Round the pier is the daily swim for Brighton Sea Swimming Club, as you may be aware.
As someone who regularly swims a fair distance out to sea, these things do play on the mind, especially when you look back at the beach, the people are just dots and there's nothing but deep water all around you...and then you start a manic crawl stroke back to shore before a great white has...